Tubular heater



' Nov.8, 1932. A. E. HARNSBERGER TUBULAR HEATER Filed May 9, 1930 gwtoz Alla'leyEJ/arnsbcryer am. 7M

Patented Nov. 8, 1932 UNITED STATES PATENT OFFICE AUDLE'Y E. HABNBBERGEB, OI CHICAGO, ILLINOIS, ASSIGNOR TO GYBO PROCESS COMPANY, 01 DETROIT, MICHIGAN, A CORPORATION OF MICHIGAN TUBULAR HEATER.

Application fled May 9, 1980. Serial No. 451,021.

This invention relates to improvements in tubular heaters, and has particular reference to improvements in tubular oil cracking stills wherein vaporized oils are subjected to high 5 temperatures to effect their molecular decomposition.

It is a common practice to pass vaporized oils in an elongated stream of restricted crosssection through the tubular passes, banks or 19 coils of an oil heater wherein the. oils are brought to cracking temperatures which are frequently in excess of 1000 F. The oil vapors in passin through the externally heated pipes or tu es of such apparatus contact with the heated walls while traveling at high velocity so that heat exchange takes place, the temperature of the tube walls and the velocity of the vapors having an important bearing on the. rate of heat transfer. It

20 has been observed that in high temperature oil cracking heaters wherein oil in the vapor phase is heated to conversion temperatures, for example, between 1000 and 1200 F., not only are low boiling point oils of gasoline range produced from higher boiling oils, but inaddition there are also roduced large quantities of fixed gas and ree carbon, the gas bein discharged from the heaters with the crac ed vaporized products while the carbon tends, at least, in part, to produce a hardened encrustation or coating on the inner Walls of the heater tubes which interferes with the heating efiiciency of such tubes and, also, results in relatively short life thereof. This condition is thought to be due tothe fact that while the oil vapor is passing through a highly heated tube the annular film or stratum of the oil vapor nearest or in contact with the inner wall of the tube is overheated. That is to say, that portion of the oil vapor which contacts directly with the highly heated surfaces of the heater tubes attains a temperature considerably above the desired average or mean cracking temperature, with the result that this portion of the oil vapor is overly heated producing therein violent splitting or decomposition reactions which produce the fixed or permanent gas and carbon deposition. Oil is a relatively poor conductor for heat and as a result the oil in the center or axial portion of the vapor stream passing through the heater tubes is, in fact, underheated insofar as a desired cracking temperature is concerned. This condition results in a low rate of cracking of the oil vapor for each passage of the latter through the heater, with the result that large quantities of recycle stock are produced which must be again passed through the heater for additional treatment.

To improve this condition it has been proposed heretofore to provide oil converters with tubes of relatively small diameter in order to provide but small volumes of oil vapor in any one of such tubes in comparison with the heating surface present. Small tubes, however, lead to mechanical difficu1 ties, particularly in high temperature apparatus wherein furnace temperatures of the order of 1500 to 2000 F. are employed. It has also been suggested to employ tubes of larger diameter which are capable of withstanding the severe furnace temperatures without rapid deterioration and to provide the interiors of such tubes with longitudinally extending cores which restrict the internal cross-sectional area of the tubes, which provide higher vapor velocities and limit the vapor in any one tube.

While these expediencies have improved to some degree the heating of oil vapor in a more uniform manner to a desired cracking temperature, the fundamental objections above noted with respect to lack of uniformity of heating the entire mass of oil vapor passing through the tubes still obtains, with the result that carbon deposition persists in the converter tubes and fixed gas formation is unduly high.

I have succeeded in materially improving these conditions in more uniformly heating the oil vapor passing through an externally heated tubular converter by providing the tubes of such converters with longitudinally extending cores, wherein the cores are formed externally with helical webs or fins so proportioned that they do not contact with the inner walls of such tubes, the said helical webs, fins or bafiles serving for a somewhat turbulent flow of the oil vapor through the an- 100 nular vapor passages of the tubes, enabling all portions of the oil vapor to contact with the highly heated inner surfaces of the tubes and avoiding specifically stratification of the oil vapor during its passage through such tubes.

For a further understanding of the invention reference is to be had to the following description and the accompanying drawing wherein:

Figure 1 is a vertical longitudinal sectional view taken through a tubular oil converter formed in accordance with the present invention,

Figure 2 is a transverse, sectional view on the line 2-2 of Figure 1, and

Figure 3 is a detail perspective view of the core construction.

Referring more particularly to the drawing, the numeral 1 designates a tube of the type used in connection with oil heaters or converters. These tubes are usually mounted within the masonry setting of a furnace (not shown) and the tube is preferably formed from ferrous alloys which permit the walls thereof to successfully withstand relatively high furnace temperatures for extend ed periods of operation without mechanical failure. These tubes are frequently formed from chromium alloys or other oxidation resisting metals and, again, ordinary steel tubes are specially treated or calorized to render them substantially immune to the action of high temperature furnace gases. Oil vapors are passed longitudinally through the tube when the latter is in active operation, the external temperature surrounding the tube being sufiicient to heat the oil vapor to a cracking temperature in excess of 1000 F.

To improve heat transfer between the oil vapor and the heated walls of the tube 1, the latter is provided with a longitudinally extending core 2. This core consists usually of a suitable length of pipe which may be formed from the same materials as those used in the construction of the tube 1. The inner pipe or core 2 is considerably smaller in diametr than the inside diameter of the pipe or tube 1 so that there is provided a longitudinally extending substantially annular space 3 between the adjacent walls of the tube 1 and the core 2 through which are passed the oil vapors to be subjected to heat treatment. The core 2 is supported longitudinally and axially Within the tube 1 and spaced from the inner walls of the latter by means of legs 4 which engage with the under surfaces of the tube 1. The legs are arranged at the ends of the core 2 and due to their formation offer minimum obstruction to uninterrupted vapor flow through the space 3.

The outstanding feature of the present invention resides in providing the core 2 with the helical rib, fin or web 5. In practice it is customary to form the element 5 from material known as welding rod, which may be wrapped around the outer wall of the core, as shown, and permanently secured in position by fusing or welding. Attention is particularly directed to the fact that the 'bailie 5 is so dimensioned that it does not contact with the inner wall 6 of the tube 1, but is spaced from the latter as disclosed. This provides for the high velocity flow of oil vapor at low pressure through the tube or vapor space 3 and eliminates specifically high back pressures. The bafile provides for a helical and somewhat turbulent flow of the oil vapor through the space 3 so that stratification of the oil vapor is prevented and therefore a uniform contact is obtained between all parts of the oil vapor and the heated surfaces of thetube 1.

By thus uniformly heating the oil vapor, converting apparatus is provided in which the evils due to over-cracking are minimized, namely, gas formation and carbon de osit and, conversely, the evils of under-crac ing are correspondingly minimized and higher yields of converted products produced. The core 2 may be positioned so as to extend but part way of the length of the tube 1 or it may extend the full length of such a tube or a tube bank in which the tube 1 forms a. part. I find it preferable to place the spirally or helically wrapped core in the tube or tubes occupying the high temperature zone of the converter, particularly in converters where a marked temperature diiferential exists in the furnace gases initially contacting with the converter tubes and the gases discharged from contact with such tubes. In the relatively cooler areas of such a heater a plain core or, in fact, no core at all may be used.

As a general rule, the core is placed in that portion of a tubular vapor phase oil converter wherein carbon deposition is apt to take place.

What is claimed is:

1. In apparatus for cracking oil in the vapor phase, a furnace tube adapted for the passage of oil vapor,a core positioned stationarily and longitudinally in said tube and supported therein in spaced relation from the inner walls of the tube to define a longitudinally extending substantially annular oil vapor' passageway, and a rod wrapped helically around the outer surface of said core and permanently secured thereto said rod having its outer surfaces terminated in spaced relationship from the inner walls of the tube, said helically wrapped rod serving to impart a substantially swirling movement to the oil vapor passing through said tube to eifect the uniform heatin walls of the tu e. y

2. In apparatus for cracking oil in the vapor phase, a furnace tube through which oil vapor is adapted to be passed and subjected to cracking temperatures, a core positioned stationarily and axially within said and contact thereof with the I pipe member and. comprising a straight elongated cylindrical body of substantially uniform diameter throughout its length, a rod wound helically around the outer surface of said body and permanently secured thereto, the outer surfaces of said rod terminating in spaced relationship from the inner walls of said tube, and radial supports projecting from said body and engaging with the inner walls of said tube to position said body centrally and axially of the tube.

3. A core for oil vapor cracking tubes, comprising a straight elongated cylindrical body of substantially uniform diameter throughout its length and adapted to be stationarily positioned in atube, a rod wrapped helically around the outer surface of said body and permanently secured in fixed relationship therewith by welding, and a plurality of spacing lugs projecting radially from said body and disposed between the windings of said r0 4. A core for tubes for converting oil in the vapor phase comprising a cylindrical body of substantially uniform diameter, a substantially helical bafiie positioned externally of said body, supporting means secured externally of said body and adapted to support the same in spaced relation with and in a converting tube, said supporting means hav ing a greater radial dimension measured from the axis of the body than any of the generatrices of said baffle.

In testimony whereof I afiix my signature.

AUDLEY E. HARNSBERGER. 

